Melatonin photoreactivity: phosphorescence formation and quenching processes

Kristján Einar Guðmundsson, Guðrún Marteinsdóttir, Kristberg Kristbergsson, Ágúst Kvaran*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Studies of melatonin photoreactivity in water solutions: An effect of an external heavy atom I on UV/Vis absorption, fluorescence and phosphorescence spectra is explored. The data allowed determination of relevant energetics for the system.The heavy atom effect (HAE) of I on melatonin is clearly found to induce an intersystem crossing from the lowest energy singlet state to the lowest energy triplet state (T1) by a state mixing. Lifetime for the first excited triplet states of melatonin in association with I and quenching rates for halomethanes (CH2X2, CHX3, CY4, X = Cl, Br, Y = Cl) are determined from Time-Correlated Single-Photon Counting decay curves for the phosphorescence. Dramatic alterations in quenching rate constants with quenchers as CH2X2 < CHX3 < CX4 and Cl < Br are attributed to energy transfer from an I−…Me*(T1) complex to low-lying electronic states of the halomethanes followed by dissociation to form R and X fragments. Relevance of the melatonin photoreactivity to photosensitizer properties in organic media is discussed. Graphical abstract: [Figure not available: see fulltext.].

Original languageEnglish
Pages (from-to)5253-5265
Number of pages13
JournalChemical Papers
Issue number8
Publication statusPublished - 13 May 2022

Bibliographical note

Funding Information:
The financial support of Rannís and the Technological Developments Fund (Grant No. 186857-0611) and the University Research Fund, University of Iceland, is gratefully acknowledged.

Publisher Copyright:
© 2022, The Author(s).

Other keywords

  • Intersystem crossing
  • Melatonin
  • Phosphorescence
  • Photosensitizer
  • Quenching


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